A conventional solar cell structure with a p-type (p-doped) base has a negative electrode that is typically on the front-side or sun side of the cell and a positive electrode on the back-side.
During the formation of a silicon solar cell, an aluminum paste is generally screen printed and dried on the back-side of the silicon wafer. The wafer is then fired at a temperature above the melting point of the eutectic point of aluminum and silicon to form an aluminum-silicon melt. Subsequently, during the cooling phase, an epitaxially grown layer of silicon is formed that is doped with aluminum. This layer is generally called the back surface field (BSF) layer, and helps to improve the energy conversion efficiency of the solar cell.
Most electric power-generating solar cells currently used are silicon solar cells. Process flow in mass production is generally aimed at achieving maximum simplification and minimizing manufacturing costs. Electrodes in particular are made by using a method such as screen printing from a metal paste.
In recent years, attention has been focused on improving the ability of silicon wafers for solar cells to convert solar energy into electrical energy, and a variety of attempts have been made to improve the electrical characteristics, such as the open circuit voltage (Voc), of back-side aluminum electrode. For example, attempts have been made to improve electrical characteristics by incorporating glass in an aluminum paste for forming a back-side aluminum electrode film, as disclosed in U.S. Pat. No. 7,771,623.